It is proposed to investigate whether the failure of immunosurveillance-related mechanisms in virus- and chemical-induced syngeneic tumors is related to the presence of large cell-surface glycoproteins which might modulate or mask tumor specific transplantation antigens (TSTA's). Transplantabilities, absorptions of anti-TSTA antisera, cell-surface macromolecular structures and topographical features in immunosensitive and immunoresistant sublines of Moloney virus- and methycholanthrene-induced tumors will be compared. Procedures will include immunochemical and electron microscopic examination of intact cells; proteolysis of viable cells to remove non-labelled or radioisotope-labelled surface components; electrophoretic and chromatographic fractionations of glycoproteins; and chemical, immunochemical and serological analyses of isolated components.